Diagnostic Performance of Photoplethysmography-Based Smartwatch for Obstructive Sleep Apnea

Considering the prevalence and health effects of obstructive sleep apnea (OSA), early diagnosis and proper treatment are essential. Polysomnography (PSG) has limitations in diagnosing or tracking large-scale OSA patients. Smartwatches (SWs) can be equipped with a photoplethysmograph (PPG) that can indirectly measure heart rate and blood oxygen saturation by detecting the difference of light absorption through blood. The purpose of this study is to compare oxygen saturation parameters of PPG-based SWs with those of PSG to determine the diagnostic accuracy for OSA.

After obtaining voluntary consent from patients who were scheduled to undergo PSG in a sleep clinic due to suspected OSA, they were randomly assigned to wear a Galaxy watch4 (GW) or Apple watch7 (AW) on their wrist. The agreement rates between the oxygen saturation parameters of the two SW types and PSG were evaluated. The accuracy, sensitivity, and specificity of the oxygen saturation parameters for diagnosis of OSA (apnea-hypopnea index [AHI] ≥5/h) were compared between the two types of SW.

A total of 133 patients underwent PSG while wearing an SW. Including duplicates, 109 patients wearing a GW and 69 wearing an AW were included. The diagnostic accuracy of AHI ≥5/h according to oxygen saturation time measured by a GW was less than 90%, the respective sensitivity and specificity were 82.9% and 75.8%. The area under the curve (AUC) of the receiver operating characteristic (ROC) curve was 0.807 (p<0.001). Using the lowest oxygen saturation value of GW, the sensitivity was 81.6%, the specificity was 69.7%, and the AUC of the ROC was 0.849 (p<0.001). The diagnostic accuracy of AHI ≥5/h according to the average oxygen saturation of AW, and the sensitivity and specificity were 75.6% and 70.8%, respectively. The AUC of this ROC curve was 0.757 (p<0.001). Using the lowest oxygen saturation value of AW, the sensitivity was 71.1%, the specificity was 62.5%, and the AUC of the ROC was 0.705 (p=0.005).

This study found that the two types of SW showed considerable accuracy in diagnosing OSA, but the accuracy decreased as the severity of OSA increased.